1. Facing & Center Drilling
MACH 118: Lathe & Mill I
Thaddeus Stevens College of Technology
Machine Tool Technology

2. Introduction FACING AND CENTER DRILLING
Facing and center drilling the workpiece are often the first steps taken in a turning project to produce a stepped shaft or a sleeve from solid material.
Much lathe work is done in a chuck, requiring considerable facing and some center drilling.

3. After completing this unit, you should be able to…
OBJECTIVES
After completing this unit, you should be able to…
Correctly set up a workpiece and face the ends.
Correctly center drill the ends of a workpiece.
Determine the proper feeds and speeds for a workpiece.
Explain how to set up to make facing cuts to a given depth and how to measure them.

4. Setting Up For Facing FACING AND CENTER DRILLING
Facing is done to obtain a flat surface on the end of cylindrical workpieces or on the face of parts clamped in a chuck or face plate.
Work is most often held in a three- or four-jaw chuck.

5. Setting Up For Facing FACING AND CENTER DRILLING
Fig. I-152 Setting up round stock in an independent chuck with a dial indicator.
Round stock can be set up using a dial indicator.

6. Setting Up For Facing FACING AND CENTER DRILLING
Square or rectangular stock can be set up either with a dial indicator or by using a tool-holder turned backward.
Fig. I-153 Rectangular stock being set up by using a toolholder turned backward. The micrometer dial is used to center the workpiece.

7. Setting Up For Facing FACING AND CENTER DRILLING
Fig. I-156 Internal chucking position.
Fig. I-157 External chucking position.
Fig. I-155 Normal chucking position.
Workpieces can be chucked:
Normally.
Internally.
Externally.

8. Facing FACING AND CENTER DRILLING
Facing from the center out produces a better finish, but it is difficult to cut on a solid face in the center.
Fig. I-158 Facing from the center to the outside of the workpiece.

9. Facing FACING AND CENTER DRILLING
Heavier cuts may be taken when facing from the outside, and it is easier to work to the scribed lines on the circumference of the work.
Fig. I-159 Facing from the outside toward the center of the workpiece.

10. Facing FACING AND CENTER DRILLING
Machining should not be done on workpieces extending more than three x dia. from the chuck face.

11. Facing FACING AND CENTER DRILLING
The tool point should be set to dead center.
Fig. I-160 Setting the tool to the center of the workpiece using the tailstock center.

12. Facing FACING AND CENTER DRILLING
The tool point should be set to dead center.

13. Facing FACING AND CENTER DRILLING
The carriage may be locked when taking facing cuts.
Fig. I-161 Carriage must be locked before taking a facing cut.

14. Facing FACING AND CENTER DRILLING
Facing to length may be accomplished by trying a cut and measuring with a hook rule or by facing to a previously made layout line.
A more precise method is to use graduations on the micrometer collar of the compound.
Fig. I-162 Facing to length using a hook rule for measuring.

15. Facing FACING AND CENTER DRILLING
The compound slide is set parallel to the ways.
The carriage is locked in place & a trial cut taken with the micrometer collar set on zero index.
Fig. I-163 The compound set at 90 degrees for facing operations.
Fig. I-164 Close-up of the compound set at 90 degrees.

16. Facing FACING AND CENTER DRILLING
The workpiece is measured with a micrometer & the desired length is subtracted from the measurement.
The remainder should be removed by facing.
A short trial cut (about 1/8”) should again be taken on the finish cut and adjustment made if necessary.
Cuts can vary considerably, depending on machine size, horsepower, tooling, and setup.

17. Facing FACING AND CENTER DRILLING
Quite often the compound is kept at 30 degrees for threading purposes.
At this angle the tool feeds into the face of the work in. for every .002 in. that the slide is moved.
Fig. I-165 The compound set at 30 degrees.
Fig. I-166 Close-up of the compound set at 30 degrees.

18. Facing FACING AND CENTER DRILLING
Both right-hand and left-hand facing tools are used for facing work held on mandrels.
Care should be taken when machining pressure is toward the small end of a tapered mandrel.
Excessive pressure may loosen the workpiece on the mandrel.
Fig. I-171 Work held between centers on a mandrel can be faced on both sides with right- & left-hand facing tools.

19. Speeds FACING AND CENTER DRILLING
Speeds (rpm) for lathe turning are determined in essentially the same as speeds for drilling tools.
Work diameter is used instead of drill diameter.
In facing operations, outside diameter of the work-piece has greater surface speed than its center.
The rpm should vary as the tool is moved in or out.
Two or three speed changes may be required to get a uniform surface finish, depending on the size of the work.

20. Center Drills And Drilling
FACING AND CENTER DRILLING
Center Drills And Drilling
When work is held and turned between centers, a center hole is required on each end of the work.
It must have a 60-degree angle to conform to the center and have a smaller drilled hole to clear the center’s point.
Facing the workpiece is almost always necessary before center drilling.
An uneven surface can push sideways on the fragile center drill point and break it.

21. Center Drills And Drilling
FACING AND CENTER DRILLING
Center Drills And Drilling
Center drills are usually held in a drill chuck in the tailstock.
Workpieces are most often supported & turned in a lathe chuck for center drilling.
Fig. I-172 Center drilling a workpiece held in a chuck.

22. Center Drills And Drilling
FACING AND CENTER DRILLING
Center Drills And Drilling
Long workpieces are generally faced by chucking one end and supporting the other in a steady rest.
The greater the work diameter & the heavier the cut, the larger the center hole should be.
Fig. I-173 Center drilling long material supported in a steady rest.

23. Center Drills And Drilling
FACING AND CENTER DRILLING
Center Drills And Drilling
Fig. I-174 Correct and incorrect depth for center drilling.
Drilling too deeply causes the center to contact only the sharp outer edge of the hole, a poor bearing surface.
It soon becomes loose & out of round, causing chatter and roughness.
Center drills often are broken from feeding the drill too fast with the lathe speed too slow or with the tailstock off center.

24. Questions?